A lithium secondary battery is known that is provided with positive and negative electrodes having materials (active materials) capable of reversibly storing and releasing lithium (Li), and which is charged and discharged by the migration of lithium ions between the electrodes. The demand for this type of lithium secondary battery is continuing to increase for use as a vehicle-mounted power supply or as power supplies of personal computers, portable terminals and the like. In particular, since lithium ion batteries are lightweight and allow the obtaining of high energy density, they are expected to be preferably used as high-output, vehicle-mounted power supplies.
A typical example of an active material used in an electrode (typically, a positive electrode) of a lithium secondary battery is a complex oxide containing lithium and a transition metal element. For example, a lithium complex oxide at least containing nickel (Ni) as the transition metal element (nickel-containing lithium complex oxide) having a layered structure is used preferably. Patent Documents 1 to 4 are examples of technical documents relating to active materials of lithium secondary batteries.